The structure and the method for suspending a shadow mask inside a color cathode ray tube has been improving with new designs of large color cathode tubes. The examples of such improvements include the structures which are revealed in U.S. Pat. No. 3,890,526 to Palac, U.S. Pat. No. 4,358,702 to Gijrath et al., and U.S. Pat. No. 4,652,792 to Tokida.
Gijrath et al.'s shadow mask support on panel 10 having skirt 11 is illustrated in FIG. 1. In the structure, shadow mask structure 20a is suspended via four plate springs 21a. Plate spring 21a is welded to peg 22a and to shadow mask structure 20a. The locations of plate springs 21a are at the four corners (or vertices) of shadow mask structure 20a. It is noted that FIG. 1 shows only one corner of the structure.
FIG. 2 illustrates Palac's device. Shadow mask structure 20b is mounted on face plate 10b via four U-shaped plate springs 21b. Each of pegs 22b is affixed to studs 12b having an opening 13b and plate spring 21b.
Tokida's shadow mask support structure is shown in FIG. 3. Shadow mask 202C is held by elastic biases 21C, one plate of which is welded to the shadow mask frame 201 C and the other plate of which is engaged with stud 12C.
In each of the above inventions, the structures which function as springs are placed so that they exert forces which compress each of the shadow masks inwards, as shown by the direction of the arrows in FIGS. 1-3. The compression forces are necessary to hold the shadow masks from excessively moving or vibrating; however, the compression forces also tend to distort or to deform the shadow mask or frame. Such distortions ultimately cause incorrect landing of electron beams on the masks, resulting in images with poor color.